Method of and machine for milling threads



I Dec. 14 1926 Original Filed Jan. 11, 1924 5 sh t -sh t, 1

'Dec. 14, 1926. Q -1 ',61-1,123

' v G. E. MIRFIELD' METHOD OF AND MACHINE- FOR MILLING THREADS Original Filed Jan. 11, 1924 5 sh t -Sheet 2 Hormel J.

Dec. 14,1926. f1,611,12s

0,12. MIRFIELD METHOD OF AND MACHINE FOR MILLING THREADS Original Filed Jan. 11, 1924 5 sh t -sh t, 5

Inventor; v

I Dec 11411926.

} G. E. MIRFIELD v METHOD AND MACHINE-FOR MILLINGTHREADS Original Filed Jan'. 11, 1924 5 s t s t 4 I Dec. 14,1926.

G. E. MIRFIELD 1 METHOD OF AND MACHINE FOR MILLING THREADS Original Filed Jan. 11, 1924 fill/9.5,. I 125 5 Sheets-Sheet 5 Patented Dec. 14, 1926;

UNITED STATES PATENT OFFICE.

GEORGE E. MIRFIELD, OF YOUNGSTOWN, OHIO.

METHOD OF'AND MACHINE Fort MILLING THREADS.

Original application filed January 11, 1924, Serial No. 685,545. Divided and this" application filed November 26, 1924.

sion and retraction of the spindle with respect to the cutter of the machine in accordance with a novel method of operation, and said means and method are claimed herein. Thus the present invention more particularly directed to the provision of a nove1 method of eflecting longitudinal progression and retraction of the work-holding spindle of a machine, such, for example, as

the thread millirQ machine disclosed in my said application Serial No. 685,545 and, ad-

ditionally, the provision of novel means for the accomplishment of said method. Further objects, features and characterist cs comprehended-by the invention will hereinafter more fully appear. v

As the present invention particularly lends itself to employment .in a machine of the general character of that disclosed in my said application Serial No. 685,545, I have illustrated in the accompanying drawings and will herein describe such a machine. em-

bodying a work-holding spindle in associa tion and combination with means for effecting longitudinal progression and retraction thereof in accordance with one manner of performing the present invention and operating. in conformity with my improved method, it .being understood however that' the use of the present invention is by no means confined? to the specific, machine hereployed a pair of rotatable milling cutters re-' inafter disclosed as the invention readily lends itself to and is suitable for use in other machines as will be apparent to those familiar with the art. V

In the aforesaid machine there are em-.

'spectively of suitable character to impart to the work a roughing cut of sufficient depth to remove the scale and true the surface which is to be threaded and toform the de- I sired'threads thereon, these cutters being so arranged in their relation to eachother and to the work that the roughing cutter oper;

Serial No. 752,289.

ates OIb the rotatin work at a point in ad vance of that at w ich the threading cutter operates there-om -Moreover for the production of a tapered thread the cutters are tapered longitudinally with respect to their axesof rotation in conformity with the taper of the thread which it is desired to produce and are of substantially the length of such thread and the threading cutter is provided with a plurality of annular teeth having the profile of the form of the desired thread but WlthOllt'PltOh, so that by effecting substantially a single revolution of the workwith respect to that cutter and simultaneously moving the work longitudinally for a distance substantially equal to the pitch of the thread to be out while effecting slight relative movement between the work andthe cutter in a direction substantially normal to the axis of the latter, a complete, tapered, accurate spiral thread of the desired length will be formed in the work.

Moreover, as more fully disclosed in my said application, the machine comprises, in operative assoclation and combination with means and lnstrumentalities to render it suitable for the performance of my im-;

proved method of milling threads as claimed 1n my'said application, Serial No. 685,545 and for effecting the longitudinal progression and retraction of the work-holding spindle in accordance with, the novel meth-I od claimed in this application, a suitable milling m'achinesuch as may be readily pur chased in the open market and embodying a removablebed or table with means for vertical and transverse adjustment thereof and an automatic longitudina feed for the table and aquick return feed therefor, the machine also having an overhanging arm arrangedto provide a bearing for the outer end of the cutter arbor as will hereinafter more fully appear.

In the accompanying drawings 1 is an end View of the organized machinein its preferred embodiment, the same being shown with the parts in initial or starting position as .atthe commencem'entof the threading operation on the work which is also shown,-

and Fig. 2 is aorearview of the machine shown in Fig. 1.; Fig. 3 is a somewhat enlarged side elevation of certain of theamech anism removed-- from the machine table, and

Fig. 41 is a similar view of theopposite side thereof, theparts being shown iin the same position as in Fig. 1 and broken away into vertical section at certain .points to better illustrate internal construction. Fig. 5 is a further enlarged top'plan view with certain parts in horizontal-section .of certain of the mechanism inoperative position 11 the ma.-

. of the same struction of a preferred form ofchuck whichmay be employed when the work to be threaded is a pipe or other hollow object, while Fig. 10 is a transverse section on line 10-10 in Fig. 9. Fig. 11 is a fragmentary plan .viewillustrating the operation of certain of the mechanism employed to effect the return of the main spindle to initial position after the completion of the threadin cycle,

and Fig. 12 is a diagrammatic view i1 ustrat- -ing'on an exaggerated scale the relative angular dis osition of the axis of rotation of the threa ing cutter and the axis of the main spindle when the machine is intended for the production of tapered threads. Similar symbols are used to designate the same parts in the several figures.

At this point it will be of advantage to briefly refer to the sequence of steps and the relativepositions assumed by the cutters and the work during the series of operations performed in the threading of a piece of work or during the threading cycle as it .may' conveniently be termed, as by so doing a more ready and ade uate comprehension of the construction of t e various parts of the machine and their method of operation as hereinafter described will be attained.

Assuming that a taper thread is to be formed upon one end of a pipe P, the end I of the pipe to be threaded is first chucked,

1 centered and clamped to the main spindle of. the machine .so as to move in correspondence therewith. Above this spindle but out .of vertical alignment therewith the threading cutter T- is supported on the main arbor of tliemachine so as to be driven thereby, while adjacent but out of contact with theipipe,

below the threading cutter and also out-of vertical alignment therewith, is disposed the T roughing cutter'R. Preferably both ofthese "cutters are similarly tapered longitudinally and in the same direction in correspondence with the taper of the thread-which it is de- .'sired to form, arid while the threading cutter teeth without pitch, as hitherto described, .65

isprovided with a plurality of annular form.

the roughing cutter is provided with 'longitudinally extending teeth of any suitable form for efiectinga roughing cut on the pipe to remove the scale therefrom and bring the pipe to truly circular cross section. The parts being disposed in the manner aforesaid, the pipe and both cutters are caused to rotate, preferably all in the same direction, the pipe at relatively slow speed and the cutters at relatively high speed, and the roughing cutter is moved horizontally toward the pipe for a suificient distance to cause it to enter the pipe for the requisite. depth'to produce the desired roughing cut and thereafter maintained in that position until it has traversed the 'entire'surface which -is to be threaded. As the'pipe continues to turn with respect to this cutter, the point where the cutter first entered the pipe, or in other words, the point where the roughing cut initially commenced, gradually moves around and upward toward the threading cutter and simultaneously with this movement both thepipe and the roughing cutter, while maintaining their relative position, are gradually moved horizontally in a direction to cause the pipe to approach the threading cutter in a generally tangential, as distinguished from a radial, direction untiLthe cutter enters the pipe to a depth requisite.

to form the threads, which will ordinarily, be accomplished when the pipe and cutter are in substantial vertical axial alignment.

When this point is reached, further move ment of translation of the pipe and roughing cutter is arrested and thereafter the threador cutter and the pipe remain in the same pipe which is to be threaded has been completely subjected to theaction of that cutter, thus completing the threading cycle. Moreover, during the operation of the threading cutter on the pipe, the latter is given a longitudinal movement with respect thereto at a predetermined rate of rogression and is also given a gradual and. very slight movement in a direction substantially transverse H1 relative position until that portion of the Y ,to the axis of rbtation of the cutter to effect the necessary compensation for the difference in radial ma nitude of different points 1 on the tapered .t read which is in process of formation, these several combined movements and different stepsand operations resulting in..tll8.PI0dl10t1OIl on the pipe of a continuous spiral tapered thread of a form similar to the profile of ,-the teeth on the threading cutter.

Referring now to the machine" shown in the drawings, 'thesame comprises a base 1 from which rises a pedestal2 to the upper extremity ofwhich is rigidly secured an overhanging arm 3 the free end of which'extends over the movable table or bed 4.- This. armis' provided with a depending bracket 5, slidable on ways 6 on the under side of the arm, in the lower end of which is 'journaled the outer end of the arbor 7 which, through suitable mechanism (not shown) is arranged to be driven from the main shaft 8 which may be provided with a pulley 9 for the reception of a belt extending to the source of power employed. If desired, however, the machine may be supplied with a motor drive or other means for effecting rotation of the shaft 8. The .bed 4 which is provided with ways 4 on its under side, is longitudinally slidable in a block 10 in a direction at right angles to the axis of the arbor 7 while the block is transversely adjustable, that is, in a direztion parallel to said axis on ways 10 formed ona supporting bracket 11 which in turn is carried by and vertically adjustable on ways 11 disposed on the face of the pedestal 2 and which may also be supported ad jacent its opposite or outer end on a threaded vertically ad ustable column 12 carried ma housing 12 rising from the base. It

will be understood that the machine is pro-.

vided with suitable means '(not shown) for effecting vertical adjustment of the bracket 11 and cross adjustment of the block 10 in the manner common to milling machines so that the bed may be moved both vertically and longitudinally with respect to the arbor 7 in the initial setting of the machine. Additionally, the bed itself is provided with means for reciprocating it beneath the arher, said means preferably comprising an automatic feed for moving the bed rearward-- ly or to the right when viewed as in Fig. l and a quick return feed, conveniently mannally operated, for moving it forwardly or to the left when viewed as in said figure, this latter means being operable through the I hand wheel 13 in the ordinary manner. For

throwing the automatic feed in or out, the machine may also be provided with a trip .14 which, when moved to the left from the osition shown in Fi 1. is effective to engage the feed mechanism so as to lnove the bed rearwardly and which, when thrown 1n the opposite direction from the position which it assumes when the feed is 'so engaged, is effective to throw out the feed and thereby arrest the rearward movement of the table. As the different features to which reference has hitherto been briefly made are generally embodied in ordinary milling machines and, together with the mechanism employed for accomplishing them, are well 'known and understood, further description thereof is unnecessary to an adequate comprehension of thepresent 1nventi'on.'

Upon the table 4 of the machine dispose mechanism in the nature of a fixture or attachment which more particularly may comprise a base 20 held down .by bolts 21, or in any other suitable way. This" base is of substantially elongated rectangular form and more or less adjacent its center is pro-- videdwith undercut ways 22 extending en'- erally parallel to the side edges of the as'e and in which is slidably mounted the rough-- ing cutter supporting block 23 hereinafter described. In front of the block, that 1s, more nearly adjacent the front edge 20 of the'base, the latter is provided with a ver-.

tically extending housing 24 in which "is journaled the main spindle 25, while projecting from the side of the base most near- 1y adjacent the pedestal 2 when the base is n the table are longitudinally separated brackets 26' forming supports for the drive shaft 27 which is rotatably journaled therein and extends generally parallel to the base, while on its opposite side the base may be provided with longitudinally spaced brackets through which is slidably extended the feed trip rod 29 hereinafter more particularly described. I

For supporting the roughing cutter R the roughing cutter supporting block 23 is providedwith a forwardly extending bracket 30 which may be integral with the block and in which is journaled the roughing cutter .shaft 31 on which is removably clamped the roughing cutter in any suitable way, conveniently by a clamping nut 33. In order to prevent any. springing'or whipping of the shaft the outer orioverhanging end is journaled in a support 34 carried by a bracket 35 bolted or otherwise secured to the roughing cutter supporting block as'by bolts 3G.v In order to permit the readya'emoval of the support 34 when the cutter is being changed, I may provide the bracket with also provided with a rearwardly extending,

tongue 37 at -the extremity .of which is mounted a camroller 38 adaptedfor cooperation with a horizontally disposed cam 39 rotatably mounted on a vertically extending pivot 40 carried by the rear end of the'bed. To enable adjustment of the block toward or away from the cam I prefer to a-rrange the tongue to slidably extend into, a slot 41 in the block and to provide for its longitudinal adjustment in this slot by means of an adjusting screw 42 which extends 'through'thetongue and has its forward end threaded into tne block. The rear. end of this screwvprojects through the tongue and is provided with an adjusting collar =43 carrying an indexing dial l, the arts being arranged in such manner that y .turning the collarthe screw may be screwed in or out in the block with corresponding movement of the'tongue with respectthereto, a set relative adjustment between the tongue and hanging arm 54 extending the block is of utility in regulating the depth of the roughing cut as will hereinafter apear. p The drive of the roughing cutter is effected, as hereinafter more fully described, through the medium'of a gear 45 mounted on the roughing cutter shaft which also carries another gear 46 meshing with still an; other gear 47 carried by a stub shaft 48 journaled in the block and extending through an arm 49 projectingfroin the side thereof. On the outer end of this shaft is mounteda worm 50 meshing with. a worm gear 51 splined upon the main shaft'27 so as to be capable of sliding movement thereon but J constrainedto rotate therewith. Asduring the operation of the machine the roughing cutter supporting block is moved back and forth in the ways 22,'it is necessary in' order to maintain constant and proper engagement between the worm 50 and gear 51 to provide means for moving thelatte'r on the shaftin correspondencewith the movements of the block, a result which can be conveniently accomplished by securing the gear to one-end of a flanged sleeve 52which is engaged by a fork 53 disposed at the end of a short over- 49 in'suchmann e'r that wh1le the sleeve can 1 rotate im the fork in correspondence with the rotation ofthe drive shaft, any' movement of the roughing cutter block in a di-' rection parallel to the shaft will effect a corresponding sliding movement of the sleeve and gear thereon. Thus, irrespective of the position of the block, the worm '50 and gear ,51 are constantly maintained in proper meshing engagement and the gear constrained to rotate with theishaftand actuate the worm.

' The means employedfor driving the gear 45 are hereafter more fully' described. p Rou ghi/ng cutter 'trdmsldt'z'ng meama.

. The main shaft is also employed foreffecting rotation of the cam 39-which, among other things, is'operative to advance and'retractthe' roughing cutter block "through the mediu'miof the tongue 37 a'nd'to this end the I shaft 27- is provided near its rearmost extremity with a worm 5.5 disposed-in pneshin g engagement with a'horizontally positioned worm gear 56 carriedby' a short stud "rotatablyv supported on 'the base 20. Above;

this. gear and on the same stud-ismounted thereon another gear 57 arranged to" mesh 1'159 ofthe 39, the'several parts being arwith still anether-gear 58' secured to the hub from the arm ranged in such manner that rotation of the drive shaft will be effective to rotate the cam' but at a materially lower speed. The principalfunction of the cam is .to advance the I roughing cutter supporting block and the roughing cutter toward the work at the proper time in the cycle of operations, to hold the block' in such position while the roughing cutter is operating on the work, and to retract the block to initial lRosition after the roughing cutter has comp etedits operation on the work, and the cam may therefore be of any construction suitable for accomplishing these results. In th e particular embodiment shown the cam comprises a circular horizontally disposed plate to'the rim of which is bolted a short depending segment60 cut-away on its inner face as at 60 to the desired contour and a hub 61 of suit able contour arranged beneath the plate in the plane of'the depending portion of the segment, thus providing a cam'groove 62 between the segment and the hub of suitable.

,width' to accommodate the cam roll 38. When the cam is so constructed the ,hub is operative during the rotation of the cam to move the roll forwardly at the proper time c and to hold it in advanced position for the- The cam is also provided with a dog 63 i which projects beyond its periphery and is conveniently adjustable with respect to the cam for a limited distance. This dog is of such form that at the proper point in the rotation of the cam it will contact with the preferably beveled end of-a verticall proecting finger 64 adiustably Ihounte upon and near the end of the trip rod 29 to extend in the path of the dog, so as tourge the rod forward against the resistance of the spring 65 disposed aboutthe rod and cause it to engage the free end of them'trip 14 thereby forcing the trip to a position to throw in the automatic feed for the table or bed 4, the conformation of the contacting surfaces of the dog and of the finger being such that after this result is accomplished the dog, as the cam continues its rotation, will slide free of the end of the finger.

Main spindle.

:In operation the requisite rotationof the pipe or othei 'swork is effected from the pref- -erably hollow'main spindle- 25 to which the pipe is suitably centeredand clamppd and the construction of thespindle and certain adjacent mechanism will. now lie-described. The spindle itself is disposed" abovethebase 20 and generally transversely thereof. be;-

tween the forward edge of the base and the roughing cutter and is journaled for rotation inthe housing 24 preferably througl controlled by an adjusting ring 7 5 and disposed in a housing 74 integral with and rising from the base. The interior of the head is cupped out to generally spherical contour to receive a centering ball 76 which is retained in position in the head by a collar 7 7 having a spherical inner surface and removably secured in a depresion in the forward side of the head by screws 78, the arrangement being such that the centering ball is very snugly seated in the end of the spindle but is capable of limited universal movement with -respect thereto. Toconstrain the ball to rotate with the spindle a stud'79 is extended through the head to project into a slot 80 formed in the ball while removably disposed in a tapered borein the center of the ball and projecting therefrom is a center 81 which maybe of ordinary construction, The ball is also provided with an annular preferably integral flange 82 which projects therefrom in a direction away from the head 72 and surrounds the centering point of the center 81. This flange forms a component part of the means employed for operatively securing the pipe to the spindle and will now be described.

Pipeck-uckivw, cent-raving aizd (Zr-icing means;

- While forthe purpose of chucking the pipe any suitable'means may be utilized,'l

"prefer to employ a chuck of the general char- 5 acter of that disclosed in my pending application for Letters Patent of the United States-Serial No. 439,959, filed January 26,

4 1921, now Patent 'No."1,548,7'30, issued August 4, 1925, and entitled Improvement in 0 method and ap aratusfor millingthreads, r since a chuck 0 that character is adapted to securely grip the pipe withoutdistorting it a condition essential to the production of accurate threads as if the pipe is sprun or 5 distorted by the chuck or other hol ing means employed and the threads.v formed upon it-w,hile-so distorted, the pipe will'to some extent resume its original form after the grip of the chuck is released, so that although the threaded areamay have 'pre-, sented a truly circular crosslsection after "the'threads have been formed-but before the release of the chuck, it thereafter {presents a more or keg elliptical cross section; 4 I have therefore illustrated and, as stated,

this member hasat its larger end unnecessary.

prefer to employ a chuck of the general character of that disclosed designed for disposition in the interior of the end of the pipe, and which may: comprise a plurality of balls 85 disposed in a generally cylindrical carrier 86 and operative to force radially outward against the pipe wall a plurality of blades 87 when a central generally conical member 88 carrier in a direction to force the ballsoutwardly'away from the center. As shown, a threaded region 89 extending through a correspondingly internally threaded bore in'the'--carrier;-thus, by grasping the nose or smaller end of the member which projects beyond inmy said patent is inoved into the 1 the opposite end of the carrier with a suitable wrench and rotating the member in the proper direction, the balls may. be crowded together so as to-force the blades outwardly to engage the pipe with equal pressure at a plurality of spaced points, thereby securely clamping the chuck in the interior .of the pipe without any distortion ofthelatter. i

As the chuck forms no part of the present invention save as it is utilized for of holding the pipein the threading operation, further description thereof herein is When using a chuck'of this general char- 90 the purpose.

acter in my improved machine I provide the nose of the member 88 with a central depresa sion 90 adapted to receive the point of the center 81 as well as an annular groove 91 extending around the nose and the side of which adjacent the end of 'the nose may be suitably inclined.

This groove is adapted I to receive the correspondingly beveled ends a pf a pair of spring pressed pins 92 extending inwardly at diametrically opposed points through the annularflange 82 and surroundedv by arotatable collar 93 disposed thereabout between a shoulder 94 on the flange and a covering plate 95 secured'to the outer extremity thereof (see Fig. 9). The-interior of, the collar is hollowed out to form a recess for the reception of the heads of the pins and their actuating springs 96 which are arranged to constantly urge the pins out-wardly and is provided with oppositely disposed similar cam surfaces 97 of suitable contour to move the pins simultaneously inwardly against the resistance of the springs when the collar is rotated. Thus, by rotating the 'collarin one direction the pins can be caused to withdraw from the space within the flange 82 to permit the nose of the mom;- ber 88 to be entered therein, the chuck of course having been previously seated in and clampedto the pipe, after which by rotatingthe'collar in the other direction, the pins may be caused to progressively enter the Q gr6ove*.91 and-by coaction with the beveled sides thereof .to draw the nose of the mem J "ber 88 against-the pointof the center 81 tween firmly clamp it thereto, thus accurately centering the chuck and in turn the pipe and locking it in, such centered position, and for efi'ecting rotation of the pipe in correspondence with the rotation of it? spindle, the

cover plate 95 is provided wi an outwardly projecting dog 98' adapted to enter belzany two ot a plurality of spaced lugs 99 wit which the end of the carrier is pro- M ruin spindle actuating means. I

'The rotation of the main'spindle 25 is ef-.

fected through the medium of a worm gear 100 dispbsed i meshing engagement with a wor 101 011 t e forward end of the main drive s iaft 27. This gear, is provided with "air integraL hub 102 having a peripheral groove tor reception of a fork 103 formed at the end of a bracket 104 integral with the base, and is splined o the spindle by a key. or spline 105 so as to rotate therewith while permitting the spindle to slide longit-udinally through the gear. Thus, irre the spindle,the gear by reason of its being supported'from the fork is constantly mamspective of any longitudinal movement of .tained in mesh with .the worm and adapted to rotate the spindle in correspondence with the rotation ot the drive shaft.

During the threading cycle as hitherto stated, the spindle and inturn the pipe is moved longitudinally for a suflicient distance to produce a thread of the desired pitch upon the pipe and for'efiecting this result I equal to that of the thread to be formed and to arrange this thread for cooperation with a suitable nut whereby relative rotation between-the spindle and the nut is efiective to move .the spindle longitudinally," assuming the nut to e stationarily supported, at a rate ofFlinear progression directly "corresponding to the pitc of the thread. 1 Under these conditionsa single relativerevolution of the spindle with respect to the nut is thus effective to -move the spindle longitudinally v -55,

for a distance equalto the pitch of the thread, that is, if the master'thread on the :at this. point for itsre'ception and thereby providing a "small shoulder 111 at the'rear end of the thread which is adapted to abut spindle is of ten pitch or ten threads to the inch, a single revolution of the s indle re--.

sults in moving the latter longitudinally for one-tenth of an inch. This method ofmoving the spindle is open to the disadvantage that in case the 'master thread'is not entirely he error transmitted to the spindle perfect, I 1s noti in ly .the error in a single convolutionofthema'ster thread but the sum 0 the.

,is in the errors of all the convolutions thereof. For example, if the error in each convolution of the master thread is .001" and the thread is of ten pitch to the inch, the error in the longitudinal movement of the spindle proproduction of accu rate threads in the work.

In accordance with my invention, however, this difliculty .is obviated b providing the spindle with a master threa of greater duced by a single relative revolution between it and the nut wilh be tentimes .001 or .01" instead of merely .001", a condition .which' is-inimical to the pitch than the thread to be formed in the 7 Work and then eflecting the requisite longitudinal movement of the spindle by a partial relative revolution between 'it and the nut instead of'by acomplete revolution.

Thus, for example, if the master thread beformed with a pitch of one to the inch and it be desired to form a thread of ten pitch to;

the inch, the requisite longitudinal movement of the spindle may be effected by cans ing a relative revolution between the nut and the spindle ofonly one-tenth of a complete turn, so that instead of the sum of all the errors in the master thread being communicated to the spindle but one-tenth of such sum iscommunicated thereto. The utilization of a master thread of greater pitch than that of the thread to be formed also'results in a minimization of error in the latter for the additional reason that, as a practical matter, a master thread of-such character, the conyolutions or segments of which. are ordinarily of relatively great cross sectional .area, can be machined more accurately than v the finer master threads hitherto employed threads is ordinarily initially greater and" I can be preserved for a. much longer period of time with corresponding resulting acourac Iii accordance with these principles I therefore provide the spindle 25 with an external master thread of greater pitch than, the thread which I desire to 'form on in the threads formed by the machine.

the pipe, for example, a pitch of one thread pitch'thread. This thread I dispose on the spindle in the rear of 'thehead 72 conveniently enlarging the diameter of the spindle the' face of the housing 24 when the spindle o sition shown. in Fig. 8'. This thread which'may be either single or multiple, is cooperative with a correspondingly internally threaded nut 112-positioned be 1 tweengthe adjacent end1faces of the housings 'to the inch when it is desired to form a ten 24 and 74 so as to be incapable of movement in a direction parallel to its axis although free for rotation about the spindle, and integral with this nut or rigidly secured thereto 1s a gear 113 in meshing engagement with a similar gear 114 keyed to a sleeve 115-journaledfor rotation in a w b 116 which extends vertically upward f om and is integral with the base and with the housing 24. he gear 114 is-disposed between the face of the web and the ratchet collar 117 which may be mounted keyed to the sleeve'and provided with l peripheral ratchet teeth 117, while adjacent the collar and pivotally mounted for rotation on the sleeve is a 'pawl arm 118 rovided ,with a spring pressed pawl 119' adapted forengagement 'with'the ratchet teeth,

the free end of the arm extending in a generally downward direction from the sleeve. Upon'the opposite side of the Web and also keyed to the sleeve is a clutch member 120 1 having clutch. teeth 120 on its 'end face adapted for cooperative engagement with sim1lar teeth on the end for rotation upon .one end of a plunger shaft 122 extended through sleeve 115 and surrounded at its other end by a coil spring 123 maintained in posltlon by nuts 124 in such manner that the spring tends to maintain inmesh the dlutch teeth on the gear and on the clutch member. The gear 121 is in meshing engagement with a gear 125' splined to the spindle for sliding "movement thereon and rotation therewith in a manner similar'to thegear 100, and the face of gear 121 is made of somewhat greater width than the face ofgear 125 so that ir-- respective of whether the clutch teeth'are' in clutc- A enga em'ent so that the gear is locked to the h member to rotate the latter, or are raised out of engagement with said teeth as when the clutch is being'rotated independently of the gear as hereinafter described, gears 121 and 125 will remain constantly in mesh.

' The clutch teeth on the clutchmember and the gear 121 are so designedthat when I engaged, as shown in'the drawings, gear 125 isefiective to drive gear 121 in the direction indicated by the arrow, thus-driving nut 112, through "sleeve 115,.gear-114 and gear 113, in the same direction as that in which the spindle is rotated by gear 100 in the threading operation.-

It 15, however, of rotation of the nut shall bear a certain definite relation to that, of the spindle in order that-the linear progression-of the latter shall bear the proper ratio to the movement of rotation thereof so that for each complete revolution of the spindle, and in turn the work, the work will be moved longitudinally of the cutter for ea-distanceequalato the pitch of the thread to be formed. In other .words,,assum ing a' thread of ten pitch to the .end in view. Thus, in th face of a gear 121,

"24 each timethat the spindle v tween the important that-the speed inch is desired and that the master thread is one pitch to the'inch, it the work one-tenth of an'inch' for each revolution of the work, and it is therefore necessary to design the ratio of the gears in the train through which the nut is driven with this e example given, the gear 125 may be provided with 54 teeth, gear 121 with teeth and both gears 114 and 113 with any similar number of teeth such as 57. Under these conditions it will be apparent tion of the spindle the.. nut will be turned for nine-tenths of a revolution or through an angle of 324, with the result that the spindle will be moved through the nut for one-tenth-of an inch, that is, for one-tenth of the pitch of the master thread. It will of course be understood that other gear ratios may be employed to effect the same result with a master thread of similar pitch andfurther that with a master thread of di tferent pitch it will ordinarilybe necessary to utilize gearing of still other ratios, the ul timate object tcY'be, atained in any case being to effect through a partial revolution of the nut for each complete revolution of the spindle, a longitudinal movement of the latter'for a distance equal to the pitch of the thread to be cut. 1

' "Spindle retumz'ng; means;

is necessary to move longitudinally of the cutter for that forceach complete revolu- I ing position, as shown in Fig. 8, to fi nal 130- I sition, substantially as shown in Fig. 9, suitable means for returning starting position are: provided. While said means may be of any convenient form, it is, however, of extreme importance that they be of a character to of the shoulder 111 with the face of housing is returned so as-to always bring thespindle to est in exhotly the same position and-thus i hsure that the forward movement of the spindle will be always initiated from exactly the same point for each threading cycle with resulting accuracy and similarity in the threads produced on consecutive pieces of work, irrespective of any slight .wear or looseness beparts of the spindle actuating mechanism. I

or attaining this result the means which- I prefer to use compris'ealink 127 pivoted to the free end of the pawl arm 118 and to oneend of ahorizontally movable lever 128 pivoted at its other end on a stud 1290M? ried by the base.

'the spindle to effect positive engagement- This lever may be pro-'. .vided near its pivoted end with an eye 130 in which'isarranged a-perforated block 131.

through which slidably extends a. rod 132 surrounded by a coil spring 133 "and at-- jtached to which is one end of anotherspring normally such that the end of the ratchet arm extends generally toward the rear of the machine, and from this position the lever maybe swung forward by the action of a trigger 135 pivoted near its center to the base, and having one end pivoted to the rod and the other extending over the edge of the abse for actuation by a stop 136 which may besecured tov the main pedestal 2, the several parts bein v so .designed that when the table moves to t e rear the tri ger will slide over the stop without actuating lever 128, but when the table is drawn forward the trigger will engage the stop and swing the lever in a similar direction,- thus causing the pawl arm to'turn the ratchet collar and in turn the sleeve and gear 114 through a suitable are;

I As the return movement of the. table -4-'is efl'ected when the ower is turned off from the machine (as will hereinafter more fully appear in the description of the operation thereof) the main spindle 25 under these conditions is locked against rotation and gear 121 similarly locked, so that as the pawl arm 118 rotates sleeve 115 in a direction opposite to that in which the clutch teeth are I designed to lock the clutch member and gear 121 together, the teeth on the member ride,

oyer those on the gear, shaft 122'sliding longitudinally in the sleeve againstthe resistance, of spring 123 for a sufficient-distance to permit such relative movement of the teeth but being immediately moved by the spring to a position. to again lock the teeth together as soon as the rotation of the sleeve is com-' pleted.

It w ll thus be apparent that rotation of vthe gear 114 through the movement imparted to the sleeve by the pawl arm is operative'to rotate nut 112 ,in the same direction as thatin which it was rotated when the spindle was advancing, and as the nut is prevented from longitudinal movement through its engagement with housings 24 and 74th'e result "of its rotation is to return flthe spindle toward its starting position unat some *point til shoulder 111 contactsv with the face of thehousing 24 and thus prevents further movement oflthe spindleinthe return direction, durin which, of course, the spindle has slid longitudinally through gears 100 and125. v r

As it would be practically impossible to design and operate the various parts so,that

,the forward movement ol':- the pawl arm would be arrested simultaneously with the movement of the spindle, I prefer to provide iirpthe linkage through which the pawl arm actuated, a suitable yieldploye'd for. thispurpose, whatever be their specific construction, being preferabl ing connection such as is efiected in the pres- I jchara'cter as to maintain .the

tion in the linkage can take up any further a motion impartedfrom the trigger 135 without injury to the parts by the rod 132 slid- 'ing through the block 131 against the resist-- ance of spring 133 until the trigger passes the stop 136, after which springs 133 and 134 operate to pull the lever 128 rearwai d and in turn swing the pawl 'arm in a similar direction to its normal position substaning this movement merely riding over the ratchet teeth without. imparting any movement-thereto. v

Main shaft driving means.

'tially as shown in Fig. 1, the pawl 119 dur- It will have been observed that the main 1 I spindle and cam 39 are driven from the main shaft 27 and this shaft in turn may bepreferably driven from the roughing cutter shaft and the latter from the main arbor 7 in any convenient manner, as for exam ple, through the medium of a gear 140" mounted on the arbor 7 and which neshes with a floating idler gear 141 in turn meshing with the gear 45 carried by the roughing cutter shaft The idler gear may be supportedin any suitable way and by any suit.-

able means such, as apair of spaced links 143 each pivoted at one end on the main which another'pair 'of substantially similar links 145 depend-and are in turn ivotally mounted attheir'ends'fon the stud the roughing cutter shaft. Thus when so supported, the idler is always maintained and on 3 arbor and at the other on a short shaft or stud 144 on which the'idler turns and from in mesh with both gears 140- and 45 irrespective of the position to which either. the roughing cutter shaft or the table-4'may be ments of reciprocation in the operation of the machine, and it will be apparent that rotation of, the arbor 7 will be operative to drive the main shaft 27 through the train comprising gears 140, 141, 45, 46, 47, worm 50- and worm gear 51, and further that when the arbor 7 is stationary the drive shaft 27 will be prevented from rotation and, in turn,

may, if desiredpbe effected in any other brought by reason of their. respective movesuitable and convenient way, the means 'emshaft stationary when the mainarbor is in similar condition as just explained.

Angular disposition of main spindle.

In a tapered thread the radial distance from the axis of the piece-to similar points on different thread-segments variesin accordance with the taper; thus, the distance, or radial magnitude as it may conveniently be termed, from the tops or apices, for example, of two adjacent thread segments to the axis of the piece is slightly different though measured in the sameradial plane. It is therefore necessary in milli ng such threadsto provide means for imparting to "the cutter or the work, simultaneously with their relative longitudinal androtative movements, a very gradual and slight movement generally transverse to the axis of the work so as to compensate for .this',difi'erence in radial magnitude by progressively causing the cutter to take a slightly deeper or lighter cut in accordance with the direction in which the relative longitudinal movement of the cutter and the work is effected, as in the ab sence of such transverse movement the cutter, upon completion of a single complete circuit of the surface of the work, would thereafter either cut into thethreads already formedor else not be eifectiveto cut a full thread on the ensuing circuit. This compensation I prefer to effect by inclining the longitudinal axis of the spindle so as to parallel the taper of the threading cutter instead of mounting the spindle on the base 20 with itsaxis parallel to the axis of the arbor 7 but since, under ordinary conditions, suchangular disposition of thevspindle is very slight, no attempt has been made to indicatethe same inithe figures illustrating the con truction of the machine; asto doso would be impracticable, In- Fig. 12, however, "I have diagrammatically illustrated the preferred manner, of dlsposing "the spindle for the cutting of tapered threads 'and reference may be {had thereto .for a better understanding! thereof.' In this fi re the threading cutter T is shown wit a greatly exaggerated taper and the pipe P is shown as it would appear after being traversed by the threading mitten-assuming the same were not provided with teeth... The axis of the spindle is designated-by the broken line AB'which,' it will be 'noted, is parallel to the line ofcontact between the cutter and the ipewhile the-axis X,X of the arbor 7 on'w ich the'cutter is mounted i' and the axis of the pipe Y- Y are parallel.

When the parts are arranged-"in this manner in an operative machine, it'will be apparent that as the spindle progressivelyndvances or moves to tl1e'right.(Fig. 12)' the end of the cutter so that pipe will be gradually raised toward the merit of the spindle is carried,'the proper "matter "how far the move relation between the cutter and the pipe for the production of a perfect. thread will lways be maintained. Such, however, would not be the case if the axes #of the spindle and cutter we're parallel, for under such conditions as the spindle advanced the pipe would gradually recede from the cutter and thereby prevent the latter from cutting I .with the cutter, to provide for a .slightuni- I versal movement between the spindle and the pipe, which result is conveniently obtained by the means hitherto described whereby the pi e is secured in operatively fixed relation wlth the ball 76 which in turn I is capable. of slightuniversal movement with respect to the spindle.

Operation;

' ,In forming a tapered thread upon a pipe or other hollow, substantially cylindrical ar-' ticle in accordance with the method claimed in my said application Serial No. 685,545 and by means of a machine of the general character of that hereinbefore described, the

machine is initially so adjusted asto bring the table to the forward end of its path and the threading and rpughing cutters into the same vertical. plane but not into vertical alignment, the roughing cutter. being disposed below and considerably in the rear of the threading cutter and the cam 39 being in a position in which the' roughing cutter supporting block is retracted toward the rearof the machine. The chuck for holding the pipe-having been inserted into and clamped in the end thereof in such manner f that the nose of the member 88 extends for a suitable "distance beyond the 'end' of the pipe, the. latter, with its oppositeend supported on a suitable track or in any other convenient way so that the pipe can be freelvrotated, is brought to the machine and 'f-disposed in a-substantially horizontal position with .the nose of member 88. against the ing held in retracted position by suitable disposition of the collar 93. Thelatter is then rotated so as to force the pins into the groove 91 and draw the chuck firmly against the center and lock it thereto, the dog 98 centering point of the center 81, pins 92 be-.

"n eanwhile having entered between twooftheadjacent lugs 99 on the end of the carrier of the". chuck, thusplacing the seyeral parts of the machine and the pipe in substantially justed to bringthe pipe to the, proper height with respect to the threading cutter and the roughihg cutter set so that it will cutinto the pipe for the desired depth, power is s ied to the machine, thereby causing rotation of both the arbor 7 carrying the threading cutter and the main shaft 27 with resulting rotation of cam 39, roughing cutter, spindle 25 (with corresponding rotation of the pipe) and nut 112, the movement of the latter being effective through the train cpmprising gears 124, 119, 114 and 113 to rotate the nut 112. Cam 39 is so designed as to quickly move the roughing cutter supporting block forward; thus carrying the roughing cutter into the rotating pipe for the maximum depth of the roughing cut, and to thereafter hold the roughing cutter supporting block in such advanced position, so that after the initial forward movement of the block is affected and the cutter brought I to depth, the distance between the'axi s, of

' the cutter and the axis of rotation of the pipe remains constant until the entire surface-of the'pipe has passed beneath the .cut-

ter, when the cam operates -to retract the block and the cutter to initial orstarting position. Preferably, the roughing cutter and the-pipe are arranged to revolvein the same direction which is suchthat as thepipe rotates the point at which. the roughing cut was commenced gradually moves up-' ward so as to approach the threading cutter. Meanwhile, rotation of cam 39 has brought dog 63 into contact with finger 64, thus urging the trip rod 29 forward to engage and actuate finger 14 and cause the, latter to throw the automatic feed of the table 4 into operation, thereby causing the table Withitsattache'd mechanism to move rearward so as to carry the continuously rotating pipe toward the threading cutter. As the pipe is gradually carried against the cutter in the manner described, the latterfinally attains the requisite depth ofv cut to form the threads and I prefer to so adjust the machine that this condition will be broughtabout when the axes of the pipe and cutter-are in substantial vertical alignment. Furthermore, the several relative movements of. the cutters and the pipe to which I have'just re ferred are sotimed with respect 'to each other, and the'relative positions of the cutters and pipe are such, that the pipe is causedto rotate through an angle of substantially 90 following the commencement of the roughing out before the threading cutter aches its maximum-depth,-with the result 'tliat- ,tl iis cutter commences and continues its operation throughout the threading cycle on a surface from which the-scale has been removed, which has been'tapered in .accordance with the taper of the thread to be formed, and which has been brought to axes of the pipe and of the cutter are in sub-' stantial vertical, alignment, a suitable stop 150, operatively fixed with respect. to the table, actuates the trip 14 so as to disengage the feed and arrest further rearwardmovement of the table, which subsequently remains at rest until the pipe has completed a little more than a full revolution with respect to the threading cutter so that the latter is accorded an opportunity to operate on the en'- tire surface to be threaded. Theoretically,

' a single complete revolution of the pipe with respect tothis cutter would be effective for this result, but in practice it is desirable to give the pipe slightly more than a full revolution with respect thereto in order to prevent' any unevenness or inequalities in the thread segments at the points of juncture be tween those portions formed by the initial operation of the cutter and those, formed by the final operation, and, in practice, revolution of the pipe through an arc of 5 to 10 will ordinarily be sufficient for this purpose.

Additionally, since the pipe begins to revolve and the roughing cutter commences its .cut considerably in advance of the time when the threading cutter is brought to depth at a point already traversed by the fore mer cutter, it is requisite, in 0rd r to per- ,rnit the action of the threading cut r on the entire surface to be threaded, to implzeirt to the pipe sufficient additional rotation yond that actually required for the operation of the threading cutter to compensate for the time that the threading cutter was inoperative after therevolution of the pipe began,

I and as the angle between lines drawn to thecenter of the pipe from the centers of both cutters when the latter are. in to depth is preferably substantially 90, the required additional rotation is substantially similar in amount. Thus, to enable both cutters to properly perform their respective functions, 1t is requisite to revolve the pipe, after the roughing cutter has been brought to depth; for a complete revolution of 360, plus 90, plus the slight amount desirable for insuring perfect joining ofthe "thread-seg- Y ments, or approximate1y455 to 460in all,

tween the master thread and the nut, or at and it will thus be apparent that during-the total revolution of the pipe the threading cutter will not be completely operative during approximately the first quarter revolution of the pipe and that the roughing cutter will be inoperative during approximately the final quarter revolution\thereofj 4 At the initiation of the threading-cycle the spindle 25 is positioned with the shoulder 1 l abutting the face of the housing 24 land.

uring the cycle is progressively adv d from such position through coaction "of nut 112 with the master thread on the spindle so as to correspondingly move the pipe longitudinally toward the left when vieweda s in Fig. 2, and as the longitudinal progression ofigthe pipe for each complete revolution is, as previously explained, equal to the pitch of the thread to be formed, the tireadi'ng cutter, instead of merely forming 'apluralityof adjacent grooves in the pipe in planes normal to its axis, is, effective to produce on the pipe in a single complete revolution thereof with respect to the cutter, a continous spiral threadof a taper corresponding to that of the cutter and of a length determined by the elfectivdlength of the, cutter; It will be observed that as, following the completion of each threading operation, the return mechanism for the spindle is effective to snugly seat the shoulder 111 against the housing 24:, any lost motion beother points of the mechanism, is-taken up before the spindle starts to rotate and move from starting position in the ensuing cycle rate operation, and further that as each time starting position, the threading operation.

so that before the cutters come into action on the pipe the various parts and particularly the master thread and the nut are snugly brought together and coordinated for accuthe spindle is returned to'exactly the same is commenced each time at the samepoint on consecutive pieces of work. 1

It will be further observed that by reason of the slightly angular disposition of the axis of the spindle with respect. to "the axis I of .the threading cutter, the pipe as it is rotated and moved longitudinally is simultaneously gradually moved toward the axis of the cutter as the spindle advances, thus compensating for the difi'erences in radial magnitude 'of the thread segments of the'tapered.

thread which is being formed and preserving at all times during the cutting operating the proper. relative positions of the cutter and of the work necessary for the production of a. perfect "thread of that character. ,will' be understood, however, that if the machine is designed for cutting straight--- threads instead of tapered threads such compensation is notrequired as the radial magnitude of all of the thread segments in the straight-thread is the same, and therefore a ed, the power is thrown off of the machine so that all parts will be brought to rest with the table 4 at the extremity of its rearward movement. The collar 93 is then loosened and the pipe, carrying the chuck, withdrawn from the machine, thespindle ofcourse remaining in itsadva-nced position. The operator, by means of the handv wheel 13 or other means provided, then operates the quick return feed so as to move the table forward to its initial or starting position during which movement the trigger 135 enga es the stop-136 so as to swing the lever 128 orward about its pivot substantially to the position shown in Fig. -11 which is effective to cause the pawl 119 to rotate the ratchet collar 117 and,.in turn, to -rotate the gears 114 and 113 with consequent rotation of the nut 112 in the same direction as that in which it was driven while the pipe was bemg threaded. Since the man arbor 7' is now stationary, the main'drive shaft 27 is also stationary and the gear prevented from rotation, so that as the master nut'is turned (and belng. as it is,inca'pable of longitudinal movement between the'hous'ings 2 1.3116]. 74) the spindle, sliding through the gears 124 I and 100, is retracted until the shoulder 111 contacts with the face of the housing 24:,

thus arresting further A movement of the spindle.

As it is desirable to insure the complete andpositive return of the spindle to initial 1 position each time that the mechanism functions, the throw of the trigger 135 is preferably so calculated as to move have 128- forward'in excess of the distance ne essary to turnnut'I12 the required amount to return the spindle, and the arts so arranged through the medium 0 the yieldingconnection'between the 'leverand link that when the lever has moved forward enough to bring shoulder 111 against the housing 24, the rod 132 thereafter merely slides through the' block against the resistance of spring133 until the point "of the trigger clears stop 136 when springs 133 and 134 immediately respectively expand and contract so as to again move the leverrearward and cause the pawl to ride over the teeth" of the ratchetto assume its-normal position as in Figs, 1- and 3, as hitherto explained.

Thelengthof the are through which the nut 112 must turntoreturn the spindle to starting position 0'f-.course will vary with the pitch ofthe master thread and the longitudinal distance through which the spindle is movedduring the threading cycle, but generally speaking the nut will, for this purpose, be turned through an are approximate 1 equal to the difference between 360 and the degrees of are through which it has been turned for each revolution of the spindle, multiplied by the total number of complete revolutions and fractions thereof which have been made by the spindle in its forward progression. Or, in other words, if for each revolution of the spindle, the nut has been turned for nine-tenths of a revolution as the spindle has moved forward, the return of the spindle can be accomplished by moving the nut in the same. direction one-tenth of the total number of degrees through which the spindle has turned; thus, for example, using a master screw of one pitch to the inch and cutting a ten pitch thread on the pipe in a machine such as herein described, it is necessary for returning the spindle to rotate the nut substantially one tenth of 455 to 460 if that be the total number of degrees through which the spindle is turned during its forward movement. However, in practical'operation, the exact calculation 'of the are through which the nutmust be turned is not required provided the means employed therefor are so designed and adjusted, preferably in the manner herein described, as to turn the nut for at least the required amount and thereafter absorb any excess motion of the parts without injury thereto.

After the table, b means of the quick return feed, has been rought to starting position and the spindle also returned to such position, the machine is once more-in condition for operation on another piece of pipe,-

cam 39 having already moved the roughing cutter supporting block and. roughing cutter rearward to starting position, preferably immediately after the roughing cutter has completed its work upon the pipe and before the completion of the work of the thread-- ing' cutter thereon.

While I have illustrated in the accom panying-drawings and have herein described with considerableparticularity one form of machine embodying a work-holding spindle and means for effecting longitudinal progression and retraction in "accordance with the present invention, it is to be understood that -the use of the presentinvention is in no way confined toa machine of that general character, the invention being readily adaptable to other forms of machines and for use under different operative .conditions and with different classes of'w'ork, and further ments empl that the detailsofdesign, construction and arrangement of the various parts and eleanism opera le in accordance with the imoyed in the provision of a mech-- proved method herein claimed maybe varied materially from the precise embodiments herein disclosed, without departing from the spirit and scope of the invention as defined in the appended claims.

Having thus described my invention, I

claim and desire to protect by Letters Pat-' movement of the spindle with respect to the cutter including a thread carried by the spindle and a nut cooperative with the thread, means for preventing'movement of the nut in a direction parallel to the axis of the spindle, means for causing a partial revolution of the nut on the spindle simul taneously with each complete'revolution of the spindle, and means distinct from said last mentioned means for rotating the nut relatively to the spindle when the spindle is stationary.

2. A machine of the class edscribed comprising a threading cutter,'a table movable with respect to the cutter, means for moving the table, a work holding rotatable spindle supported from the table and movable therewith, means including a worm and worm gear for rotating the spindle, said worm and worm gear being operative by mutual coaction to lock the spindle against rotation when said rotating means are stalUU tionary, means for causing longitudinal movement of the spindle with respect to the cutter andcomprislng a thread carried by the, spindle and a nut .cooperative with the thread, means for rotating the nut when the Q spindle is rotating, and means distinct from said last mentioned means for causing a partial revolution of the nut relatively to'the spindle when said spindle against rotation.

is held locked .3. A machine ofthe class described, comprising'a' cutter rotatable in a fixed position, a table movable with respect to the cutter, a spindle journaled forv rotation above the table, means including a worm and worm gear operative to rotate the spindle 1n a predetermined direction and to lock the spindle against rotation by interaction of said worm and worm gear when said means are stationary, a thread carried by the. spindle, a nut cooperative withthe thread, means for constraining the nut tov otate in a fixed position, means for rotating the nut in the same direction as the spindle while the latter is being rotated, and means for rotating the nut in the samedirection while the spindle is -locked.'

4. machine of the class described com prising a cutter rotatable in a fixed position, a table movable with respect to the cutter, a work holding spindle journaled for rotation above the table, means for rotating the spindle in a predetermined direction in- I and constrained to rotate in a fixed position,

means for effecting a partial revolution of the nut for each complete revolution of the spindleand in the same direction so as to effect a longitudinal advance of the spindle in a predetermined amount simultaneously with each revolution thereof, and means for imparting to the nut a further partial revolution when the spindle is locked against rotation to thereby return the spindle toits initial position{ 5. A machine as specified in claim 4 and embodying a fixed stop adapted to limit the return movement of the spindle andincluding an 'overrunning clutch in the spindle returning means. a

6. A, machine as specified in claim'4 and embodying a fixed stop and a shoulder on the splndle adapted to engage the stop and limit the return movement of the spindle,

said spindle returning means being arranged to positively move said shoulder into engagement with said stop upon each return movement of the spindle.

7. The method of effecting a longitudinal progression of the work-holding spindle of a milling machine for an amount for each revolution of the spindle equal to-the pitch of the thread to be milled, which consists a lead thread of. one-tenth the pitch of the in imparting tothe spindle, provided with thread to be milled, a single complete revolution-in a given direction and simultaneous- 1y im eating to a nut cooperative with said threa a movementof; revolution in the same directiorr through are of substantially 324 while restraining. the nut from end wise movement.

a. In mechanism, a rotatable spindle,

means fonrotating the spindle, a thread on" the s indle, a nut cooperative with the threa means for preventing longitudinal movement of the nut, means forrotating a the nut in the same direction that the spindle is rotated but at a slower rate, whereby when the spindle and the nut are both rotated the spindle will be advanced longitudinally through the nut, means forming a component part of the spindle rotating means operative to'lock the spindle against rotation when it has accomplished a desired longitudinal advance, means for imparting additional rotation to the nut while the spindle is locked whereby the spindle is retracted longitudinally and means limit-- ing the extent to which the spindle can be retracted.

9. In mechanism, a rotatable spindle, means for rotating the spindle, a thread on the spindle, a nut cooperative with the thread, means for preventing longitudinal movement of the nut, means for rotating the nut in the same direction that the spindle v the spindle at the same point 10. The meth d of effecting longitudinal progression and retraction of a threaded spindle, which comprises effecting rotation of the spindle within a'threaded nut, simultaneously eflecting rotation of the nut in the same direction asthe spindle but at a slower rate while restraining the nut against longitudinal movement wherebythe spindle is caused to advance through the nut, locking the spindle. against rotation when it has attained apredetermined advanced'position and then rotating the nut for an additional amount in the same direction to thereby cause the spindle to be retracted to a predetermined position. v a

In witness whereof I have hereunto set my hand this 24th day of November A. D., 1924.

GEORGE E. MIRFIELD. 

